1. Field of the Invention
The invention relates to apparatus for drilling a well bore into the earth using a system comprising a drilling rig with a top drive/kelly or a downhole motor for rotating the drill string comprising interconnected joints of drill pipe. More close, it relates to apparatus for uninterrupted flushing a well bore while a drill pipe joint is being added to or removed from drill string. More particularly it relates to apparatus in systems which use for uninterrupted flushing a plurality of valves being included in the drillstring for temporarily bypassing flushing fluid flow while making a connection.
2. Description of Related Art
In drilling, as the operation continues, it is necessary to add sections of drill pipe, during which time in conventional drilling circulation of drilling fluid must be discontinued. It leads to several complications in the well bore and lost of time.
For many years drilling industry is working on technical solutions which could provide for uninterrupted flushing a well bore while making a drill string connection.
The known continuous circulation methods and apparatus comprise two main groups.
The first group deploys a plurality of continuous flushing valves also referred to as “drill string couplings,” “continuous circulation subs”, “continuous circulation valves”. The second group deploys for continuous circulation a dividable chamber sealed around drill pipe as it is disclosed in U.S. Pat. No. 3,559,739 to Hutchison.
The present invention relates to the first group.
U.S. Pat. No. 1,491,986 to Greene discloses a valve assembly, a continuous circulation coupling comprising housing adopted for including in the drill string as a sub such that every stand receives a valve assembly. A hinged flapper valve with two seats is placed inside the housing. The housing has a threaded side opening. The arrangement is such that the flap valve will normally cover the side opening but may pivot to close axial channel of the valve. Normally the side opening is covered with a plug. When it comes to making a connection, the plug is unscrewed from the valve body and a bypass line (a hose) is screwed into the side opening (side port). By operating appropriate valves on surface lines the direction of circulation is changed. Now the drilling fluid flows from the side port. Axial channel above the side port is sealed by the flap. The driving mechanism is disconnected from the drill string. A new drill pipe stand is added to the drill string. Again, by operating appropriate valves the flow of the drilling fluid is diverted to normal axial direction; the bypass line is disconnected; the side port is sealed with the plug; and drilling is resumed.
U.S. Pat. No. 2,158,356 to Dyer discloses some new features to the design of the flapper valve.
U.S. Pat. No. 3,298,385 to Jackson et.el. (“Constant circulating coupling device”) pointed at a number of disadvantages inherent in the continuous circulating sub of the patent . . . 356. Patent . . . 385 discloses a continuous circulating sub with a one piece housing; a removable flapper valve; a bayonet-type lock between side port and bypass line and between the side port and a plug.
UK patent GB 2 427 217 to Calderoni et. el. discloses a device which uses the same operational process as the devices of the above cited patents. But the device of the patent . . . 217 has two valves. Valve A closes and opens a side port. Valve B closes and opens the axial channel. In preferred embodiment, the valves are flapper-type (named in the patent “throttle”). No specifics concerning side port connecting mechanism and a plug (“safety plug”) of the side port are disclosed or claimed.
An important issue with continuous flushing devices which deploy flapper-type valves is that drilling fluids flow through open seats of the valve. If drilling fluid is a mud composed of clay, barite, loss circulation additives these materials unevenly deposit on sealing surfaces. It may lead to partial closure of the valve, leaks, complications while drill string connection process and unsafe conditions on the rig floor.
U.S. Pat. No. 7,308,952 to Strazhgorodskiy discloses a system for continuously flushing a wellbore while drilling and making drill string connections with direct or reverse circulation of a drilling fluid or with a formation fluid being produced through the drill string. The continuous flushing system of the . . . 952 deploys a ball valve. But the ball valve in preferred embodiment of . . . 952 may be difficult to manufacture and maintain. In addition, the valve of . . . 952 lacks a feature which would exclude unwonted movements of the valve ball while drilling.
The incessant for almost hundred years, but with a few practical results, attempts to develop reliable apparatus for continuously flushing wells while making drill string connections, show the importance of the technology for the industry.
3. Objects and Advantages
An object of present invention is to provide an apparatus for continuously flushing a well bore while making drill string connections. More specifically, the apparatus using a ball-type valve which provides the possibility to drill with direct or reverse circulation, is contained in full open position while being in the well, has convenient means for connecting a bypass line to the side port, and which has supplementary safety features.